Spark-plug.



A. SCHMIDT.

SPARK PLUG.

N Fl

APPL 7.1917. 1,271,620. Patented July 9,1918,

Jvwemtoz fllbcr A e/Z772 ii ammm ALBERT SCHMIDT, OF FLINT, MICHIGAN, ASSIG-NOR TO CHAMPION IGNITION COMPANY, OF FLINT, MICHIGAN, A CORPORATION OF MICHIGAN.

SPARK-ZELUG.

Specification of Letters Patent.

Patented July 9, 1918.

Application filed April 27, 1917. Serial No. 164,842.

To all whom it may concern Be it known that I, ALBERT SCHMIDT, a citizen of the Republic of France, residing at Flint, in the county of Genesee and State of Michigan, have invented certain new and useful Improvements in Spark-Plugs, of which the following is a specification, reference being had therein to the accompanying drawings.

The invention relates to spark-plugs, and has particular reference to a construction in which the insulated electrode is readily removable and which also-provides compensation for the difierential expansion of the metal and the. insulator.

In the drawings:

Figure 1 is a central longitudinal section through the spark-plug;

Fig. 2 is a cross section on line mm Fig. 1.

A is a metallic casing provided with the usual threaded nipple B for engagement with the engine casing, and C is the insulator secured within the casing, preferably by providing a shoulder D and an opposed shoulder E, the metal of. the casing being closed therearound while hot to form a gas tight seal. F is an insulated electrode which passes through the central aperture in the insulator, being inserted from the inner end thereof and having a shoulder G for bearing thereagainst. H is a clamping nut engaging the threaded outer end of the electrode to clamp the same to the insulator.

On account of the difference in coeflicients of expansion of the insulatin material and the metallic electrode, it is di cult to maintain a tight joint under varying conditions of temperature. To compensate for this, instead of clamping directly against the outer end of the insulator the nut H bears upon a sleeve I which extends inward in a counterbore, thereby lessening the distance between the opposed points of bearing on the insulator. There is, however, danger that the shoulder against which the inner end of the sleeve bears may be overstrained, causing the cracking of the insulator. I have therefore provided a construction in which the sleeve I is threaded, as at J, and

this threaded portion is engaged with corresponding threads formed within the insulator. The number of bearings formed by successive convolutions of the thread are sufficient to distribute the stress from the sleeve I into the body of the insulator C, thereby avoiding sharply-localized stresses and also avoiding danger of breaking. Furthermore, the threads form good heatconducting contact between the insulator and the sleeve, which assists in dissipating the heat of explosion.

If desired, the sleeve may be formed of material having a difi'erent coeflicient of expansion from that of the electrode so as to compensate for the-differential coeflicient of expansion of the insulator and metal.

What I claim as my invention is: 1. In a spark-plug, the comblnationw1th an insulator, of an electrode extendlng therethrough, a metallic sleeve surroundin saidelectrode and having a different coe cient of expansion, said sleeve having a threaded engagement with the insulator, and clamping means for said electrode engaging the outer end of said sleeve.

2. Ina spark-plug, the combination with an electrode, of an insulator through which said electrode passes, being formed with an inner portion for fitting the electrode and a portion having a bore of greater diameter and internally threaded at its inner end, a sleeve or bushing surrounding said electrode correspondingly threaded and engaged w1th the threaded portion of the insulator, andclamping means upon said electrode for engaging the outer end of said sleeve or bushing.

In testimony whereof I aflix my si ature. ALBERT SC DT. 

